1. Field of the Invention
This invention relates to a pipe propelling apparatus suited for constructing a pipeline in the ground and, more particularly to, an apparatus for propelling a plurality of pipes arranged in series in the ground.
2. Description of the Prior Art
A pipe propelling apparatus for constructing a pipeline in the ground generally comprises a shield tunnelling machine for excavating earth and sand and a basic thrusting mechanism for pressing sequentially a plurality of pipes into a space obtained by excavating the earth and sand by the tunnelling machine such as to dispose the pipes in the space while advancing the pipes together with the tunnelling machine.
According to the pipe propelling apparatus of this type, a thrust or driving force is applied to the rearmost pipe from the basic thrusting mechanism to advance all pipes together with the tunnelling machine. Therefore, the thrust necessary for advancing the pipes and tunnelling machine is increased in proportion to the total length of pipes to be propelled, i.e., a distance between vertical shafts. As a result, a large thrust acts on the pipes, particularly on the rearmost pipe. When the large thrust acts on the pipe as mentioned above, it is liable to break the pipe. If the mechanical strength of the pipe is enhanced in order to prevent the pipe from breakage, the cost of the pipe becomes high. Thus, when the pipeline is constructed in the ground by the pipe propelling apparatus, the distance between the vertical shafts cannot be enlarged.
To overcome the problem as noted above, there is proposed a pipe propelling apparatus which is provided with an intermediate thrusting mechanism for applying the thrust as mentioned above to one pipe other than the rearmost pipe.
This pipe propelling apparatus gives the thrust not only to the rearmost pipe, but also to one of intermediate pipes through the intermediate thrusting mechanism. However, according to this pipe propelling apparatus, the intermediate thrusting mechanism has to be finally disassembled and removed, and therefore this pipe propelling apparatus can be applied when constructing a pipeline of such size that an operator can enter.